In German Offenlegungsschrift No. 3 128 111, there is described an apparatus for producing open-sided V-belts from a sleeve-shaped roll which has been pre-vulcanised. The roll is located over two rollers which are axis-parallel to one another. One of the rollers is subsequently moved away from the other roller so as to increase the axial spacing between the rollers. The roll of material is tensioned during such movement and, whilst tensioned, is cut into individual V-belts which do not require any further processing treatment.
It is necessary to tension the vulcanised roll on the rollers for the cutting operation, but such tensioning has, in practice, proved difficult to achieve. A very high degree of accuracy is needed when cutting V-belt blanks which are already vulcanised. The blanks are in the form of a sleeve-shaped roll. The cutting operation has to be performed within a tolerance of 0.1 mm. This is because, if the belts are used in motor vehicles, any greater inaccuracy in cutting causes the V-belts to produce considerable and unacceptable background noise.
V-belt blanks which are already vulcanised are, obviously, extremely rigid. Additional problems arise when trying to cut the blanks because it is formed from rubber layers or plies which are highly resistant to abrasion. The V-belts need not, however, be pre-vulcanised. Instead, they may be covered with a coating in the form of a very stable, rubberised or rubber-coated fabric to increase abrasion resistance. Such a manufacturing process is, however, complicated because every single V-belt has to be covered with a coating so that it can then be subjected to a vulcanising process in a mould. During vulcanisation in the mould, inaccuracies in respect of dimensions can, in the main, be compensated for with the result that highly accurate cutting operations for unvulcanised V-belts are not necessary.
Due to the disadvantages of the coating stage of this method, there is an increasing tendency for open-sided V-belts to be produced by cutting a vulcanised roll.
However, in adopting this approach, it is necessary to overcome the major problem of the guiding of the rotating, vulcanised roll in a very smooth manner so that an accurate cutting can be achieved.